C#: JSON Serialization of List<CustomClass> returns empty array?

Question

So, I have a custom class 'User' like this:

class User
    {
        string firstname;
        string lastname;
        string proposedname;
        public User(string firstname, string lastname)
        {
            this.firstname = firstname;
            this.lastname = lastname;
            this.proposedname = $"{firstname}.{lastname}".ToLower();
        }
}

And another Class "UserCreator that has a method "GenerateList" and a method "WriteList" as well as a field which is simply a List :

public class UserCreator
    {
        internal List<User> Users;
        public UserCreator(int n = 1000)
        {
            Users = new List<User>();
            this.GenerateList(n);
        }
       public  void WriteList(string outputPath)
        {
            string json = Newtonsoft.Json.JsonConvert.SerializeObject(this.Users, Newtonsoft.Json.Formatting.Indented);
            System.IO.File.WriteAllText(outputPath, json);

        }

        void GenerateList(int amount)
        {
            List<User> result = new List<User>();
            ///...
            this.Users = result;
        }
    }

Everything works just fine until it get's to the Serialization part in WriteList(). Instead of working as Intended I get something like this:

[
  {},
  {},
  {},
  {},
  {},
  {},
  {},
  {}
]

I'm guessing it has to do with the fact that I'm using a List of a custom Class. Is that a known limitation of Newtonsoft.Json? Or maybe due to Access modifiers?

Answer 1

How you have declared your class is completely encapsulating all of your User data.

Instead of properties, those are instance fields (or class members, if we're being picky), and by default these are private. Instead, take care of your access modifiers and at least expose a public getter for every property, like so:

public class User
{
    public string firstname { get; private set;}
    public string lastname { get; private set;}
    public string proposedname { get ; private set; }
    public User(string firstname, string lastname)
    {
        this.firstname = firstname;
        this.lastname = lastname;
        this.proposedname = $"{firstname}.{lastname}".ToLower();
    }
}